OK....A few people have responded with the idea that I did something to break the cart. I didn't.
Here's the scoop.....The ballast box was on my tractor in the garage when I loaded the box onto the cart. I "dropped" the box onto the cart knowing that it weighed roughly 600lbs. Therefore, I did it slooow and eeeasy. I am not so dumb as to slam that much weight down on ANYTHING.!!!!....Including my garage floor.
Now, my garage is 24ft. wide. I was centered in the bay and I rolled the ballast box roughly just 6' to the middle of the garage. 6 feet. Then, I tried to roll it 6' back to the center of the bay and got about 3' before the wheel broke. Think about what I just said in that paragraph....I rolled it a total of about 9'. It's not like I am rolling it all the way downtown for God's sake.
And, about rateing a weight load. However and whoever rated this dolly is a flunky. Stoned too. It is on wheels, therefore you cannot rate the dolly as a "static" rate. In other words, the manufacturer can't say it's a 1000lb. dolly, just don't try to roll it with that much weight on it. THAT would be ridiculous.
And, IMO, tractor supply is at fault here. They should not be selling inferior products. They need to know that the product they sell has stand up to it's rateings. Otherwise, there is a safety issue, which indeed was the case with my story and experience. It could have easily landed on my toe. Glad it didn't.!!
Also, about price.....I am not a cheap skate. I am not an engineer so I, being the consumer, have to believe the product has been tried and tested.
The product is JUNK. Period. Can't we all see that.?? I guess not.
I would be dissapointed with the service life of the product. 9 feet isn't very far.
Stuff usually breaks for a reason, but it is rare for a manufactured product with wide distribution to be seriously over rated. It is of course possible that one of the wheels was defective from the factory.
I always try to figure out how stuff happens. I have broke enough stuff that I have gotten plenty of practice in the last 40 years.

And I always try to figure out all the possibilities so I can avoid making the same mistake twice, on the rare chance that if it was my own fault.
There is one possibility that comes to mind that I haven't seen anyone address yet

Working as a mechanical designer for 40 years makes me look at things a little differently than some folks. For the following reason I would never have designed a cart to hold a 600 pound weight with castors that are only good for 300 pounds each.
The problem may have been caused when you lowered the box onto the cart. If any part of it touched down on one corner for even a fraction of a second before the other three corners it could have placed a momentary 600 pound load on one wheel.
The wheels that are only rated for 300 lbs of weight. Under those circumstances it is probable that the wheel components would become stressed beyond their yeild strength, causing failure. Once one wheel fails, the cart will tilt, lifting the oposite diagonal wheel off the ground, placing 300 lbs of weight on the remaining 2 wheels, at the very limit of the design capacity cusing them to fail also, but probably not as quickly.
My rather limited experience with 3 point attachments, hitches and top link adjustments would seem to support the possibility that things are not always perfectly level front to back and side to side when lifting and lowering them with a 3 point. Even a slight varience in the concrete floor of as little as a quarter inch under a tractor tire or the cart wheel could cause an overload condition. The only sure way to be able to set down a solid 600 pound object on a wheeled cart without hurting it is to get a cart that has wheels that are rated for 600 pounds each so momentary loads caused by floor variations and or link adjustments will be adequetly supported.

The product may of course just be "junk" as you have stated



However there is a good chance that its design capacity of one of the components was at one point exceeded, leading to total failure of the assembly for reasons previously stated.




chit happens but it usually happens for a reason...
junk happens usually because of the lowest bidder in the supply chain
